SEP-973: Expose additional metadata for Implementations, Resources, Tools and Prompts

Expose additional metadata for Implementations, Resources, Tools and Prompts

Final

Standards Track

Field	Value
SEP	973
Title	Expose additional metadata for Implementations, Resources, Tools and Prompts
Status	Final
Type	Standards Track
Created	2025-07-15
Author(s)	@jesselumarie
Sponsor	None
PR	#973

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Abstract

This SEP proposes adding two optional fields—icons and websiteUrl. The icons and websiteUrl would be added to the Implementation schema so that clients can visually identify third-party implementations and link directly to their documentation. The icons parameter will also be added to the Tool, Resource and Prompt schemas. While this can be used by both servers and clients for all implementations, we expect it to be used initially for server-provided implementations.

Motivation

Current State

Current implementations only expose namespaced metadata, forcing clients to display generic labels with no visual cues.

Proposed State

The proposed implementation would allow us to add visual affordances and links to documentation, making it easier to visually identify which servers/clients are providing an implementation e.g. a tool in a slash command interface:

• Visual Affordance: Icons make it immediately clear to users which tool or resource source is in use.
• Discoverability: A link to documentation (websiteUrl) allows clients to direct users to more information with a single click.

Rationale

This design builds on prior work in web manifests (MDN) and consolidates community feedback:

• Consolidation of PRs: Merges the changes from PR #417 and PR #862 into a single, cohesive enhancement.
• Flexible Icon Sizes: Supports multiple icon sizes (e.g., 48x48, 96x96, or any for vector formats) to accommodate different client UI needs.
• Optional Fields: By making both fields optional, existing implementations remain fully compatible.

Specification

Extend the Implementation object as follows:

/**
 * A url pointing to an icon URL or a base64-encoded data URI
 *
 * Clients that support rendering icons MUST support at least the following MIME types:
 * - image/png - PNG images (safe, universal compatibility)
 * - image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)
 *
 * Clients that support rendering icons SHOULD also support:
 * - image/svg+xml - SVG images (scalable but requires security precautions)
 * - image/webp - WebP images (modern, efficient format)
 */
export interface Icon {
  /**
   * A standard URI pointing to an icon resource.
   *
   * Consumers MUST takes steps to ensure URLs serving icons are from the
   * same domain as the client/server or a trusted domain.
   *
   * Consumers MUST take appropriate precautions when consuming SVGs as they can contain
   * executable JavaScript
   *
   * @format uri
   */
  src: string;
  /** Optional override if the server’s MIME type is missing or generic. */
  mimeType?: string;
  /** e.g. "48x48", "any" (for SVG), or "48x48 96x96" */
  sizes?: string;
}

/**
 * Describes the MCP implementation
 */
export interface Implementation extends BaseMetadata {
  version: string;
  /**
   * An optional list of icons for this implementation.
   * This can be used by clients to display the implementation in a user interface.
   * Each icon should have a `kind` property that specifies whether it is a data representation or a URL source, a `src` property that points to the icon file or data representation, and may also include a `mimeType` and `sizes` property.
   * The `mimeType` property should be a valid MIME type for the icon file, such as "image/png" or "image/svg+xml".
   * The `sizes` property should be a string that specifies one or more sizes at which the icon file can be used, such as "48x48" or "any" for scalable formats like SVG.
   * The `sizes` property is optional, and if not provided, the client should assume that the icon can be used at any size.
   */
  icons?: Icon[];
  /**
   * An optional URL of the website for this implementation.
   *
   * Consumers MUST takes steps to ensure URLs serving icons are from the
   * same domain as the client/server or a trusted domain.
   *
   * Consumers MUST take appropriate precautions when consuming SVGs as they can contain
   * executable JavaScript
   *
   * @format: uri
   */
  websiteUrl?: string;
}

Extend the Tool, Resource and Prompt interfaces with the following type:

  /**
   * An optional list of icons for a resource.
   * This can be used by clients to display the resource's icon in a user interface.
   * Each icon should have a `kind` property that specifies whether it is a data representation or a URL source, a `src` property that points to the icon file or data representation, and may also include a `mimeType` and `sizes` property.
   * The `mimeType` property should be a valid MIME type for the icon file, such as "image/png" or "image/svg+xml".
   * The `sizes` property should be a string that specifies one or more sizes at which the icon file can be used, such as "48x48" or "any" for scalable formats like SVG.
   * The `sizes` property is optional, and if not provided, the client should assume that the icon can be used at any size.
   */
  icons?: Icon[];

Backwards Compatibility

Both icons and websiteUrl are optional fields; clients that ignore them will fall back to existing behavior.

Security Implications

This shouldn’t introduce any new security implications.